Mixed ionic conductor and device using the same

ABSTRACT

A mixed ionic conductor with an ion conductive oxide has a perovskite structure of the formula Ba a (Ce 1−b M 1   b )L c O 3−α , wherein  
     M 1  is at least one trivalent rare earth element other than Ce;  
     L is at least one element selected from the group consisting of Zr, Ti, V, Nb, Cr, Mo, W, Fe, Co, Ni, Cu, Ag, Au, Pd, Pt, Bi, Sb, Sn, Pb and Ga;  
     with 0.9≦a≦1;  
     0.16≦b≦0.26;  
     0.01≦c≦0.1;  
     and (2+b−2a)/2≦α&lt;1.5.  
     Such a mixed ionic conductor has not only the necessary conductivity for electrochemical devices such as fuel cells, but also superior moisture resistance.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a mixed ionic conductor and anelectrochemical device, such as a fuel cell or a gas sensor, using thesame.

[0003] 2. Description of the Prior Art

[0004] The applicant has long been actively developing mixed conductorsof protons and oxide ions (see for example Publication of UnexaminedJapanese Patent Application (Tokkai) No. H5-28820 or H6-236114). Thesemixed ionic conductors are basically perovskite oxides containing bariumand cerium wherein a portion of the cerium has been substituted by thesubstitute element M, so as to achieve a high ionic conductivity(chemical formula: BaCe_(1−p)M_(p)O_(3−α)). Especially, when thesubstitution amount p of the substitution element M is 0.16 to 0.23, themixed ionic conductor has a high conductivity, higher even thanzirconia-based oxides (YSZ: yttrium-stabilized zirconia), whichconventionally have been used as oxide ionic conductors. As thesubstitution element M, rare earth elements are suitable, in particularheavy rare earth elements, because of their atomic radius and chargebalance.

[0005] New fuel cells, sensors and other electrochemical devices usingsuch materials as a solid electrolyte have been developed. The sensorcharacteristics and the discharge characteristics of fuel cells usingsuch materials have been shown to be superior to prior devices. Otherpatent applications related to these materials are Tokkai H5-234604,Tokkai H5-290860, Tokkai H6-223857, Tokkai H6-290802, Tokkai H7-65839,Tokkai H7-136455, Tokkai H8-29390, Tokkai H8-162121, and TokkaiH8-220060.

[0006] However, these materials show some problems with regard to theirchemical stability. For example, barium tends to precipitate in CO₂ gas.To solve these problems, the applicant has proposed a counter-strategyin Tokkai H8-107918. However, even this counter-strategy is not perfect,and for example at low temperatures of 85° C. and 85% humidity,precipitation can be observed in shelf tests and boiling tests in water.Moreover, under high water vapor pressures as during discharge of thefuel cells, barium can be seen to precipitate near the platinumelectrodes. Furthermore, with gas sensors, there is the problem ofmaintaining high ion conductivity at lower temperatures over a long timeand the problem of raising the acid resistance of the oxide itself.

SUMMARY OF THE INVENTION

[0007] To solve these problems, it is an object of the present inventionto improve the chemical stability of the mixed ionic conductors.

[0008] The main cause for decomposition of the oxides due to humidity isbelieved to be the fact that the segregated barium turning into bariumhydroxide reacts with the carbon dioxide, and forms stable bariumcarbonate. To increase the moisture resistance, the present inventionuses a mixed ionic conductor including the following perovskitestructure oxide.

[0009] A mixed ionic conductor of one embodiment of the presentinvention (a first ionic conductor) includes an ion conductive oxidehaving a perovskite structure of the formula Ba_(a)(Ce_(1−b)M¹_(b))L_(c)O_(3−α), wherein

[0010] M¹ is at least one trivalent rare earth element other than Ce;

[0011] L is at least one element selected from the group consisting ofZr, Ti, V, Nb, Cr, Mo, W. Fe, Co, Ni, Cu, Ag, Au, Pd, Pt, Bi, Sb, Sn, Pband Ga;

[0012] with 0.9≦a≦1;

[0013] 0.16≦b≦0.26;

[0014] 0.01≦c≦0.1;

[0015] and (2+b−2a)/2≦α<1.5.

[0016] In this mixed ionic conductor it is preferable that M¹ is atleast one element selected from the group consisting of La, Pr, Nd, Pm,Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Y and Sc. More preferably, M¹ is Gdand/or Y.

[0017] It is also preferable that L is at least one element selectedfrom the group consisting of Zr, Ti, Fe, Co, Ni, Cu, Bi, Sn, Pb and Ga.More preferably, L is at least one element selected from the groupconsisting of Zr, Ti, Bi, Pb and Ga.

[0018] A mixed ionic conductor of another embodiment of the presentinvention (a second ionic conductor) includes an ion conductive oxidehaving a perovskite structure of the formula Ba_(e)Zr_(1−z)M²_(z)O_(3−β), wherein

[0019] 0.9≦e≦1;

[0020] M² is at least one element selected from the group consisting oftrivalent rare earth elements, Bi, Ga, Sn, Sb and In;

[0021] with 0.01≦z≦0.3;

[0022] and (2+z−2e)/2≦β<1.5.

[0023] In this mixed ionic conductor it is preferable that 0.16≦z≦0.3.It is also preferable that M² is at least one element selected from thegroup consisting of trivalent rare earth elements and In, especiallyelements selected from the group consisting of Pr, Eu, Gd, Yb, Sc andIn.

[0024] A mixed ionic conductor of yet another embodiment of the presentinvention (a third ionic conductor) includes an ion conductive oxidehaving a perovskite structure of the formula Ba_(d)Zr_(1−x−y)Ce_(x)M³_(y)O_(3−γ) wherein

[0025] M³ is at least one element selected from the group consisting oftrivalent rare earth elements, Bi and In;

[0026] with 0.98≦d≦1;

[0027] 0.01≦x≦0.5;

[0028] 0.01≦y≦0.3;

[0029] and (2+y−2d)/2≦γ<1.5.

[0030] In this third mixed ionic conductor, it is preferable that M³ isat least one element selected from the group consisting of Nd, Sm, Eu,Gd, Tb, Yb, Y. Sc and In. More preferably, M³ is at least one elementselected from the group consisting of Gd, In, Y and Yb.

[0031] The mixed ionic conductors of the present invention have not onlythe necessary conductivity for electrochemical devices such as fuelcells, but also superior moisture resistance.

[0032] Throughout this specification, “rare earth element” means Sc, Y,and the lanthanides (elements 57La through 71Lu). In the above formulas,α, β and γ are determined by the absent amount of disproportionateoxygen.

[0033] The present invention also provides devices using such a mixedionic conductor. A fuel cell in accordance with the present inventionincludes as a solid-state electrolyte a mixed ionic conductor asdescribed above. A gas sensor in accordance with the present inventionincludes as a solid-state electrolyte a mixed ionic conductor asdescribed above. Using the mixed ionic conductors of the presentinvention provides electric devices, such as fuel cells and gas sensors,with high moisture resistance, high performance, and long lifetimes.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034]FIG. 1 is an exploded perspective cross-sectional view of anembodiment of a fuel cell using a mixed ionic conductor in accordancewith the present invention.

[0035]FIG. 2 is a cross-sectional view of an embodiment of a gas sensorusing a mixed ionic conductor in accordance with the present invention.

[0036]FIG. 3 is a graph showing the conductivity of mixed ionicconductors in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] The following is an explanation of the preferred embodiments ofthe present invention.

[0038] As the applicant has pointed out in the above-noted publications,the high conductivity of mixed ionic conductors in accordance with thepresent invention stems from the mixed ion conductivity of oxygen ionsand protons. In order to improve the moisture resistance of such mixedionic conductors, a suitable substitute element is introduced into theabove-mentioned first ionic conductor so as to reduce the amount ofbarium in the perovskite oxide to less than the stochiometric ratio. Inthe following, such a mixed ionic conductor also is referred to as“additive system” conductor.

[0039] The second and the third ionic conductors in accordance with thepresent invention are also mixed ionic conductors with high moistureresistance. In the following, these mixed ionic conductors are referredto as “barium-zirconium system” conductors and “barium zirconium ceriumsystem” conductors, respectively. While these systems are mixed ionicconductors exhibiting proton conductivity, they still provide highmoisture resistance.

[0040] These systems of mixed ionic conductors can be obtained withconventional raw materials and manufacturing methods. Specific examplesof manufacturing methods are explained along with the examples furtherbelow.

[0041] The following is an explanation of a device using a mixed ionicconductor in accordance with the present invention.

[0042]FIG. 1 is a cross-sectional perspective view of an embodiment of afuel cell in accordance with the present invention. This planar fuelcell has several layered units 7, which include a cathode (fuelelectrode) 3, a solid electrolyte 2 layered on the cathode 3, and ananode (air electrode) 1 on the solid electrolyte 2. Separators 4 arearranged between the layered units 7.

[0043] When generating power, an oxidation gas 6 (such as air) issupplied to the anodes 1, and a fuel gas 5 (a reduction gas such ashydrogen or natural gas) is supplied to the cathodes 3. Theoxidation-reduction reaction at the electrodes generates electrons, sothat the fuel cell serves as an electric power source.

[0044]FIG. 2 is a cross-sectional view of an embodiment of a gas sensorin accordance with the present invention. This HC sensor (hydrocarbonsensor) includes an anode 15, a solid electrolyte 14 on the anode 15,and a cathode 16 on the solid electrolyte 14. This layered structure isattached with an inorganic adhesive 18 to a (ceramic) substrate 17,providing a space 20 between the substrate and the layered structure.This space 20 is in communication with the outside via a diffusionlimiting hole 13.

[0045] When a certain voltage (for example 1.2V) is applied steadilybetween the two electrodes 15 and 16, a current that is proportional tothe concentration of hydrocarbons in the space adjacent to the anode 15is attained as output. During the measurement, the sensor is kept at acertain temperature with a heater 19 attached to the substrate. Toprovide the diffusion limiting hole 13 is advantageous to limit theinflow of the material to be measured (here, hydrocarbons) into thespace 20.

[0046] This embodiment has been explained for a HC sensor, but an oxygensensor is also possible by exchanging anode and cathode in the structureshown in FIG. 2. Furthermore, the mixed ionic conductor of the presentinvention is not limited the above, but also can be applied to all kindsof other electrochemical devices.

EXAMPLES

[0047] The following is a more detailed description of specific examplesof the present invention. It should be noted that the present inventionis in no way limited to these examples.

[0048] As examples of the present invention, oxides as shown in Tables 1to 6 have been synthesized. These oxides were synthesized by solid statesintering. An oxide powder of barium, cerium, zirconium, and rare earthelements was weighed to the composition ratio listed in the tables, andcrushed and mixed with ethanol in an agate mortar. After sufficientmixing, the solvent was removed, defatted with a burner, and crushingand mixing were repeated in the agate mortar. Then, the samples werepressed into columnar shape and fired for 10 hours at 1300° C. After thefiring, granules of about 3 μm were produced by coarse crushing, withfurther crushing in a benzene solution with a planetary ball mill. Theresulting powder was vacuum-dried at 150° C., and columns were formedwith a hydrostatic press at 2 tons/cm², which were immediately fired for10 hours at 1650° C. to synthesize a sintered product. For almost allsamples, a very compact single-phase perovskite oxide was attained. Theresulting samples were then evaluated as follows:

[0049] Boiling Test

[0050] As an accelerated test of moisture resistance, the samples wereintroduced into boiling water of 100° C., and the level of Baprecipitation was evaluated after 10 hours by measuring the pH value.This evaluation utilizes the fact that the pH value in the aqueoussolution rises proportionally with the precipitation of barium. For a pHchange of not more than 2, the moisture resistance was taken to beexcellent (A), for more than 2 and not more than 3.5, it was taken to begood (B), for more than 3.5 and not more than. 4, it was taken to beadequate (C), and for more than 4, it was taken to be poor (D).

[0051] Conductivity

[0052] After the above-mentioned boiling test, disks of 0.5 mm thicknessand 13 mm diameter were made of the columnar sintered product samples,both sides of the disks were coated with a platinum paste on an area of0.5 cm² each, which was baked onto the samples, and the ion conductivitywas measured. In this experiment, the conductivity was calculated fromthe resistance with the alternating current impedance method in air. Themeasurement temperature was 500° C. The resistance of the leads of themeasurement device was subtracted. When the conductivity (in S/cm) wasat least 0.007, it was taken as A, for at least 0.001 and less than0.007 it was taken as B, and for less than 0.001 it was taken as C.

[0053]FIG. 3 is an arrhenius plot showing the conductivity of materialsin accordance with the present invention.

[0054] Crystallinity

[0055] When the sintered product was single-phase it was taken as A,when it was multi-phase, it was taken as B, and sintering failures weretaken as C.

[0056] The tables show the conductivity at 500° C. and the result of thepH evaluation in the boiling test. TABLE 1 Material Boiling TestCrystallinity Conductivity BaCe_(0.8)Gd_(0.2)O_(3−α) D A ABa_(0.99)Ce_(0.8)Gd_(0.2)O_(3−α) D A A Ba_(0.98)Ce_(0.8)Gd_(0.2)O_(3−α)D A A Ba_(0.94)Ce_(0.8)Gd_(0.2)O_(3−α) D A BBa_(0.90)Ce_(0.8)Gd_(0.2)O_(3−α) D A B

[0057] TABLE 2 Additive System Material Boiling Test CrystallinityConductivity BaCe_(0.8)Gd_(0.2)Zr_(0.01)O_(3−α) B A ABaCe_(0.8)Gd_(0.2)Zr_(0.04)O_(3−α) B A ABaCe_(0.8)Gd_(0.2)Zr_(0.06)O_(3−α) B A ABaCe_(0.8)Gd_(0.2)Zr_(0.1)O_(3−α) B A ABaCe_(0.8)Gd_(0.2)Zr_(0.11)O_(3−α) D B not measuredBaCe_(0.8)Gd_(0.2)Zr_(0.15)O_(3−α) D C not measuredBa_(0.99)Ce_(0.8)Gd_(0.2)Zr_(0.01)O_(3−α) B A ABa_(0.99)Ce_(0.8)Gd_(0.2)Zr_(0.04)O_(3−α) B A ABa_(0.99)Ce_(0.8)Gd_(0.2)Zr_(0.06)O_(3−α) B A BBa_(0.99)Ce_(0.8)Gd_(0.2)Zr_(0.1)O_(3−α) B A BBa_(0.99)Ce_(0.8)Gd_(0.2)Zr_(0.11)O_(3−α) B B CBa_(0.98)Ce_(0.8)Gd_(0.2)Zr_(0.01)O_(3−α) B A ABa_(0.98)Ce_(0.8)Gd_(0.2)Zr_(0.04)O_(3−α) B A BBa_(0.98)Ce_(0.8)Gd_(0.2)Zr_(0.06)O_(3−α) B A BBa_(0.98)Ce_(0.8)Gd_(0.2)Zr_(0.1)O_(3−α) B A BBa_(0.98)Ce_(0.8)Gd_(0.2)Zr_(0.11)O_(3−α) B B CBa_(0.98)Ce_(0.8)Gd_(0.16)Zr_(0.04)O_(3−α) B A BBa_(0.98)Ce_(0.8)Gd_(0.23)Zr_(0.04)O_(3−α) B A BBa_(0.98)Ce_(0.8)Gd_(0.26)Zr_(0.04)O_(3−α) B A ABa_(0.9)Ce_(0.8)Gd_(0.2)Zr_(0.01)O_(3−α) B A BBa_(0.9)Ce_(0.8)Gd_(0.2)Zr_(0.04)O_(3−α) B A CBa_(0.9)Ce_(0.8)Gd_(0.2)Zr_(0.06)O_(3−α) B A CBa_(0.9)Ce_(0.8)Gd_(0.2)Zr_(0.1)O_(3−α) A A CBa_(0.9)Ce_(0.8)Gd_(0.2)Zr_(0.11)O_(3−α) A B DBa_(0.89)Ce_(0.8)Gd_(0.2)Zr_(0.01)O_(3−α) B A CBa_(0.85)Ce_(0.8)Gd_(0.2)Zr_(0.04)O_(3−α) B A D

[0058] TABLE 3 Additive System Material Boiling Test CrystallinityConductivity Ba_(0.98)Ce_(0.8)Y_(0.2)Zr_(0.04)O_(3−α) B A BBa_(0.99)Ce_(0.8)Y_(0.2)Zr_(0.01)O_(3−α) B A ABa_(0.9)Ce_(0.8)Y_(0.2)Zr_(0.1)O_(3−α) B A CBa_(0.98)Ce_(0.8)La_(0.2)Zr_(0.04)O_(3−α) B A CBa_(0.99)Ce_(0.8)La_(0.2)Zr_(0.01)O_(3−α) B A BBa_(0.9)Ce_(0.8)La_(0.2)Zr_(0.1)O_(3−α) B A CBa_(0.98)Ce_(0.8)Pr_(0.2)Zr_(0.04)O_(3−α) B A BBa_(0.99)Ce_(0.8)Pr_(0.2)Zr_(0.01)O_(3−α) B A BBa_(0.9)Ce_(0.8)Pr_(0.2)Zr_(0.1)O_(3−α) B A CBa_(0.98)Ce_(0.8)Nd_(0.2)Zr_(0.04)O_(3−α) B A BBa_(0.99)Ce_(0.8)Nd_(0.2)Zr_(0.01)O_(3−α) B A BBa_(0.9)Ce_(0.8)Nd_(0.2)Zr_(0.1)O_(3−α) B A CBa_(0.98)Ce_(0.8)Pm_(0.2)Zr_(0.04)O_(3−α) B A BBa_(0.99)Ce_(0.8)Pm_(0.2)Zr_(0.01)O_(3−α) B A BBa_(0.9)Ce_(0.8)Pm_(0.2)Zr_(0.1)O_(3−α) B A CBa_(0.98)Ce_(0.8)Sm_(0.2)Zr_(0.04)O_(3−α) B A BBa_(0.99)Ce_(0.8)Sm_(0.2)Zr_(0.01)O_(3−α) B A ABa_(0.9)Ce_(0.8)Sm_(0.2)Zr_(0.1)O_(3−α) B A CBa_(0.98)Ce_(0.8)Eu_(0.2)Zr_(0.04)O_(3−α) B A BBa_(0.99)Ce_(0.8)Eu_(0.2)Zr_(0.01)O_(3−α) B A ABa_(0.9)Ce_(0.8)Eu_(0.2)Zr_(0.1)O_(3−α) B A CBa_(0.98)Ce_(0.8)Tb_(0.2)Zr_(0.04)O_(3−α) B A BBa_(0.99)Ce_(0.8)Tb_(0.2)Zr_(0.01)O_(3−α) B A ABa_(0.9)Ce_(0.8)Tb_(0.2)Zr_(0.1)O_(3−α) B A CBa_(0.98)Ce_(0.8)Dy_(0.2)Zr_(0.04)O_(3−α) B A BBa_(0.99)Ce_(0.8)Dy_(0.2)Zr_(0.01)O_(3−α) B A ABa_(0.9)Ce_(0.8)Dy_(0.2)Zr_(0.1)O_(3−α) B A CBa_(0.98)Ce_(0.8)Ho_(0.2)Zr_(0.04)O_(3−α) B A BBa_(0.99)Ce_(0.8)Ho_(0.2)Zr_(0.01)O_(3−α) B A BBa_(0.9)Ce_(0.8)Ho_(0.2)Zr_(0.1)O_(3−α) B A CBa_(0.98)Ce_(0.8)Er_(0.2)Zr_(0.04)O_(3−α) B A BBa_(0.99)Ce_(0.8)Er_(0.2)Zr_(0.01)O_(3−α) B A ABa_(0.9)Ce_(0.8)Er_(0.2)Zr_(0.1)O_(3−α) B A CBa_(0.98)Ce_(0.8)Tm_(0.2)Zr_(0.04)O_(3−α) B A BBa_(0.99)Ce_(0.8)Tm_(0.2)Zr_(0.01)O_(3−α) B A BBa_(0.9)Ce_(0.8)Tm_(0.2)Zr_(0.1)O_(3−α) B A CBa_(0.98)Ce_(0.8)Yb_(0.2)Zr_(0.04)O_(3−α) B A BBa_(0.99)Ce_(0.8)Yb_(0.2)Zr_(0.01)O_(3−α) B A ABa_(0.9)Ce_(0.8)Yb_(0.2)Zr_(0.1)O_(3−α) B A C

[0059] TABLE 4 Additive System Material Boiling Test CrystallinityConductivity Ba_(0.99)Ce_(0.8)Gd_(0.2)Ti_(0.01)O_(3−α) B A CBa_(0.99)Ce_(0.8)Gd_(0.2)Ti_(0.1)O_(3−α) B A CBa_(0.98)Ce_(0.8)Gd_(0.2)Ti_(0.04)O_(3−α) B A CBa_(0.9)Ce_(0.8)Gd_(0.2)Ti_(0.1)O_(3−α) A A CBa_(0.98)Ce_(0.8)Gd_(0.16)Ti_(0.04)O_(3−α) B A CBa_(0.99)Ce_(0.8)Gd_(0.2)Bi_(0.01)O_(3−α) B A ABa_(0.99)Ce_(0.8)Gd_(0.2)Bi_(0.1)O_(3−α) B A BBa_(0.98)Ce_(0.8)Gd_(0.2)Bi_(0.04)O_(3−α) B A BBa_(0.9)Ce_(0.8)Gd_(0.2)Bi_(0.1)O_(3−α) A A CBa_(0.98)Ce_(0.8)Gd_(0.16)Bi_(0.04)O_(3−α) B A BBa_(0.99)Ce_(0.8)Gd_(0.2)Pb_(0.01)O_(3−α) B A BBa_(0.99)Ce_(0.8)Gd_(0.2)Pb_(0.1)O_(3−α) B A CBa_(0.98)Ce_(0.8)Gd_(0.2)Pb_(0.04)O_(3−α) B A CBa_(0.9)Ce_(0.8)Gd_(0.2)Pb_(0.1)O_(3−α) A A CBa_(0.98)Ce_(0.8)Gd_(0.16)Pb_(0.04)O_(3−α) B A CBa_(0.99)Ce_(0.8)Gd_(0.2)Ga_(0.01)O_(3−α) B A ABa_(0.99)Ce_(0.8)Gd_(0.2)Ga_(0.1)O_(3−α) B A CBa_(0.98)Ce_(0.8)Gd_(0.2)Ga_(0.04)O_(3−α) B A BBa_(0.9)Ce_(0.8)Gd_(0.2)Ga_(0.1)O_(3−α) A A CBa_(0.98)Ce_(0.8)Gd_(0.16)Ga_(0.04)O_(3−α) B A BBa_(0.98)Ce_(0.8)Gd_(0.2)V_(0.04)O_(3−α) C A CBa_(0.98)Ce_(0.8)Gd_(0.2)Nb_(0.04)O_(3−α) C A CBa_(0.98)Ce_(0.8)Gd_(0.2)Cr_(0.04)O_(3−α) C A CBa_(0.98)Ce_(0.8)Gd_(0.2)Mo_(0.04)O_(3−α) C A CBa_(0.98)Ce_(0.8)Gd_(0.2)W_(0.04)O_(3−α) C A CBa_(0.98)Ce_(0.8)Gd_(0.2)Fe_(0.04)O_(3−α) B A CBa_(0.98)Ce_(0.8)Gd_(0.2)Co_(0.04)O_(3−α) B A CBa_(0.98)Ce_(0.8)Gd_(0.2)Ni_(0.04)O_(3−α) B A CBa_(0.98)Ce_(0.8)Gd_(0.2)Cu_(0.04)O_(3−α) B A BBa_(0.98)Ce_(0.8)Gd_(0.2)Ag_(0.04)O_(3−α) C A BBa_(0.98)Ce_(0.8)Gd_(0.2)Au_(0.04)O_(3−α) C A BBa_(0.98)Ce_(0.8)Gd_(0.2)Pd_(0.04)O_(3−α) C A BBa_(0.98)Ce_(0.8)Gd_(0.2)Pt_(0.04)O_(3−α) C A BBa_(0.98)Ce_(0.8)Gd_(0.2)Sb_(0.04)O_(3−α) B A CBa_(0.98)Ce_(0.8)Gd_(0.2)Sn_(0.04)O_(3−α) B A C

[0060] TABLE 5 Barium-Zirconium System Material Boiling TestCrystallinity Conductivity BaZr_(0.84)Y_(0.16)O_(3−α) A A CBaZr_(0.8)Y_(0.2)O_(3−α) A A C BaZr_(0.75)Y_(0.25)O_(3−α) A A CBaZr_(0.7)Y_(0.3)O_(3−α) A A B BaZr_(0.65)Y_(0.35)O_(3−α) B C notmeasured BaZr_(0.8)In_(0.2)O_(3−α) A A C BaZr_(0.7)In_(0.3)O_(3−α) A A BBaZr_(0.95)Gd_(0.05)O_(3−α) A A C BaZr_(0.84)Gd_(0.16)O_(3−α) A A CBaZr_(0.8)Gd_(0.2)O_(3−α) A A C BaZr_(0.75)Gd_(0.25)O_(3−α) A A CBaZr_(0.7)Gd_(0.3)O_(3−α) A A B BaZr_(0.65)Gd_(0.35)O_(3−α) B C notmeasured BaZr_(0.84)Sc_(0.16)O_(3−α) A A C BaZr_(0.7)Sc_(0.3)O_(3−α) A AB BaZr_(0.84)Bi_(0.16)O_(3−α) B A C BaZr_(0.8)Bi_(0.2)O_(3−α) A A CBaZr_(0.75)Bi_(0.25)O_(3−α) A A C BaZr_(0.7)Bi_(0.3)O_(3−α) A A CBaZr_(0.95)Yb_(0.06)O_(3−α) A A C BaZr_(0.84)Yb_(0.16)O_(3−α) A A CBaZr_(0.8)Yb_(0.2)O_(3−α) A A C BaZr_(0.75)Yb_(0.25)O_(3−α) A A CBaZr_(0.7)Yb_(0.3)O_(3−α) B A C BaZr_(0.84)Dy_(0.16)O_(3−α) B A BBaZr_(0.75)Dy_(0.25)O_(3−α) A A C BaZr_(0.99)La_(0.01)O_(3−α) A A CBaZr_(0.95)La_(0.05)O_(3−α) A A C BaZr_(0.84)La_(0.16)O_(3−α) A A CBaZr_(0.95)Pr_(0.05)O_(3−α) A A C BaZr_(0.84)Pr_(0.16)O_(3−α) A A CBaZr_(0.75)Pr_(0.25)O_(3−α) A A B BaZr_(0.9)Nd_(0.1)O_(3−α) A A CBaZr_(0.84)Nd_(0.16)O_(3−α) A A C BaZr_(0.9)Pm_(0.1)O_(3−α) A A CBaZr_(0.84)Pm_(0.16)O_(3−α) A A C BaZr_(0.84)Sm_(0.16)O_(3−α) A A CBaZr_(0.8)Sm_(0.2)O_(3−α) A A C BaZr_(0.9)Eu_(0.1)O_(3−α) A A CBaZr_(0.82)Eu_(0.18)O_(3−α) A A C BaZr_(0.8)Eu_(0.2)O_(3−α) A A BBaZr_(0.82)Tb_(0.18)O_(3−α) A A C BaZr_(0.8)Ho_(0.2)O_(3−α) A A CBaZr_(0.74)Er_(0.26)O_(3−α) A A C BaZr_(0.72)Tm_(0.28)O_(3−α) A A CBaZr_(0.8)Ga_(0.2)O_(3−α) A A C BaZr_(0.7)Ga_(0.3)O_(3−α) A A CBaZr_(0.8)Sn_(0.2)O_(3−α) A A C BaZr_(0.75)Sn_(0.25)O_(3−α) A A CBaZr_(0.72)Sb_(0.28)O_(3−α) A A C

[0061] TABLE 6 Barium Zirconium Cerium System Material Boiling TestCrystallinity Conductivity BaCe_(0.1)Zr_(0.74)Y_(0.16)O_(3−α) B A BBaCe_(0.2)Zr_(0.64)Y_(0.16)O_(3−α) A A CBaCe_(0.4)Zr_(0.4)Y_(0.2)O_(3−α) B A ABaCe_(0.05)Zr_(0.9)Gd_(0.05)O_(3−α) A A CBaCe_(0.15)Zr_(0.65)Gd_(0.2)O_(3−α) A A CBaCe_(0.4)Zr_(0.4)Gd_(0.2)O_(3−α) B A ABaCe_(0.5)Zr_(0.3)Gd_(0.2)O_(3−α) B A ABaCe_(0.2)Zr_(0.6)Gd_(0.2)O_(3−α) A A BBa_(0.99)Ce_(0.2)Zr_(0.6)Gd_(0.2)O_(3−α) A A BBaCe_(0.35)Zr_(0.5)Gd_(0.15)O_(3−α) A A ABa_(0.99)Ce_(0.35)Zr_(0.5)Gd_(0.15)O_(3−α) A A ABaCe_(0.4)Zr_(0.45)Gd_(0.15)O_(3−α) A A BBaCe_(0.4)Zr_(0.5)Gd_(0.1)O_(3−α) A A BBaCe_(0.01)Zr_(0.7)Gd_(0.29)O_(3−α) A A CBaCe_(0.05)Zr_(0.85)Gd_(0.1)O_(3−α) A A CBaCe_(0.2)Zr_(0.65)Sc_(0.05)O_(3−α) A A CBaCe_(0.05)Zr_(0.8)Sc_(0.15)O_(3−α) A A CBaCe_(0.05)Zr_(0.85)Bi_(0.1)O_(3−α) A A CBaCe_(0.2)Zr_(0.6)Bi_(0.2)O_(3−α) A A CBaCe_(0.4)Zr_(0.55)Bi_(0.05)O_(3−α) A A CBaCe_(0.05)Zr_(0.7)Bi_(0.25)O_(3−α) A A CBaCe_(0.05)Zr_(0.9)Yb_(0.05)O_(3−α) A A CBaCe_(0.2)Zr_(0.75)Yb_(0.05)O_(3−α) A A CBaCe_(0.4)Zr_(0.4)Yb_(0.2)O_(3−α) B A ABaCe_(0.05)Zr_(0.7)Yb_(0.25)O_(3−α) A A CBaCe_(0.1)Zr_(0.6)Yb_(0.3)O_(3−α) A A CBaCe_(0.05)Zr_(0.8)Dy_(0.15)O_(3−α) A A CBaCe_(0.2)Zr_(0.7)Dy_(0.1)O_(3−α) A A CBaCe_(0.2)Zr_(0.75)La_(0.05)O_(3−α) A A CBaCe_(0.05)Zr_(0.85)La_(0.05)O_(3−α) A A CBaCe_(0.4)Zr_(0.4)La_(0.2)O_(3−α) A A CBaCe_(0.2)Zr_(0.75)Pr_(0.05)O_(3−α) A A CBaCe_(0.4)Zr_(0.5)Pr_(0.1)O_(3−α) B A CBaCe_(0.2)Zr_(0.7)Nd_(0.1)O_(3−α) A A CBaCe_(0.4)Zr_(0.45)Nd_(0.05)O_(3−α) B A BBaCe_(0.4)Zr_(0.4)Nd_(0.2)O_(3−α) B A BBaCe_(0.4)Zr_(0.4)Pm_(0.2)O_(3−α) B A CBaCe_(0.4)Zr_(0.5)Pm_(0.1)O_(3−α) B A CBaCe_(0.4)Zr_(0.5)Sm_(0.1)O_(3−α) B A BBaCe_(0.1)Zr_(0.7)Sm_(0.2)O_(3−α) A A CBaCe_(0.4)Zr_(0.4)Eu_(0.2)O_(3−α) B A BBaCe_(0.4)Zr_(0.5)Eu_(0.1)O_(3−α) B A CBaCe_(0.4)Zr_(0.4)Eu_(0.2)O_(3−α) B A CBaCe_(0.4)Zr_(0.55)Tb_(0.05)O_(3−α) B A CBaCe_(0.05)Zr_(0.8)Ho_(0.15)O_(3−α) A A CBaCe_(0.5)Zr_(0.4)Er_(0.1)O_(3−α) B A CBaCe_(0.5)Zr_(0.35)Tm_(0.15)O_(3−α) B A CBaCe_(0.4)Zr_(0.4)Ga_(0.2)O_(3−α) B A CBaCe_(0.05)Zr_(0.7)Ga_(0.25)O_(3−α) A A CBaCe_(0.1)Zr_(0.8)Sn_(0.1)O_(3−α) A A CBaCe_(0.05)Zr_(0.75)Sn_(0.2)O_(3−α) A A CBaCe_(0.4)Zr_(0.4)Sb_(0.2)O_(3−α) B A CBaCe_(0.4)Zr_(0.4)In_(0.2)O_(3−α) B A ABa_(0.99)Ce_(0.4)Zr_(0.4)In_(0.2)O_(3−α) B A ABaCe_(0.2)Zr_(0.6)In_(0.2)O_(3−α) A A BBaCe_(0.3)Zr_(0.5)In_(0.2)O_(3−α) A A ABaCe_(0.4)Zr_(0.5)In_(0.1)O_(3−α) A A ABaCe_(0.5)Zr_(0.4)In_(0.1)O_(3−α) A A ABaCe_(0.5)Zr_(0.3)In_(0.2)O_(3−α) A A ABaCe_(0.6)Zr_(0.3)In_(0.1)O_(3−α) B A A

[0062] As becomes clear from this evaluation, mixed ionic conductors inaccordance with the present invention have considerably better moistureresistance, while the ion conductivity can be held at a practical level.

[0063] The above examples have been synthesized by solid statesintering, but there is no limitation to this method, and the oxide alsocan be synthesized by coprecipitation, nitration, spray granulation orany other suitable method. It is also possible to use film formingmethods such as CVD or sputtering methods. It is also possible to usethermal spraying. There is no limitation to the shape of the oxide, andit can be of any shape, including bulk shapes and films.

[0064] The invention may be embodied in other specific forms withoutdeparting from the spirit or essential characteristics thereof. Theembodiments disclosed in this application are to be considered in allrespects as illustrative and not restrictive, the scope of the inventionbeing indicated by the appended claims rather than by the foregoingdescription, all changes that come within the meaning and range ofequivalency of the claims are intended to be embraced therein.

What is claimed is:
 1. A mixed ionic conductor comprising an ionconductive oxide having a perovskite structure of the formulaBa_(a)(Ce_(1−b)M¹ _(b))L_(c)O_(3−α), wherein M¹ is at least onetrivalent rare earth element other than Ce; L is at least one elementselected from the group consisting of Zr, Ti, V, Nb, Cr, Mo, W, Fe, Co,Ni, Cu, Ag, Au, Pd, Pt, Bi, Sb, Sn, Pb and Ga; with 0.9≦a≦1;0.16≦b≦0.26; 0.01≦c≦0.1; and (2+b−2a)/2≦α≦1.5.
 2. The mixed ionicconductor of claim 1, wherein M¹ is at least one element selected fromthe group consisting of La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm,Yb, Y and Sc.
 3. The mixed ionic conductor of claim 2, wherein M¹ is atleast one element selected from the group consisting of Gd and Y.
 4. Themixed ionic conductor of claim 1, wherein L is at least one elementselected from the group consisting of Zr, Ti, Fe, Co, Ni, Cu, Bi, Sn, Pband Ga.
 5. A mixed ionic conductor comprising an ion conductive oxidehaving a perovskite structure of the formula Ba_(e)Zr_(1−z)M²_(z)O_(3−β), wherein 0.9≦e≦1; M² is at least one element selected fromthe group consisting of trivalent rare earth elements, Bi, Ga, Sn, Sband In; with 0.01≦z≦0.3; and (2+z−2e)/2≦β<1.5.
 6. The mixed ionicconductor of claim 5, wherein 0.16≦z≦0.3.
 7. The mixed ionic conductorof claim 5, wherein M² is at least one element selected from the groupconsisting of trivalent rare earth elements and In.
 8. The mixed ionicconductor of claim 7, wherein M² is at least one element selected fromthe group consisting of Pr, Eu, Gd, Yb, Sc and In.
 9. A mixed ionicconductor comprising an ion conductive oxide having a perovskitestructure of the formula Ba_(d)Zr_(1−x−y)Ce_(x)M³ _(y)O_(3−γ) wherein M³is at least one element selected from the group consisting of trivalentrare earth elements, Bi and In; with 0.98≦d≦1; 0.01≦x≦0.5; 0.01≦y≦0.3;(2+y−2d)/2≦γ<1.5.
 10. The mixed ionic conductor of claim 9, wherein M³is at least one element selected from the group consisting of Nd, Sm,Eu, Gd, Tb, Yb, Y, Sc and In.
 11. The mixed ionic conductor of claim 10,wherein M³ is selected from Gd, In, Y and Yb.
 12. A fuel cell comprisingas a solid-state electrolyte a mixed ionic conductor of claim
 1. 13. Agas sensor comprising as a solid-state electrolyte a mixed ionicconductor of claim
 1. 14. A fuel cell comprising as a solid-stateelectrolyte a mixed ionic conductor of claim
 5. 15. A gas sensorcomprising as a solid-state electrolyte a mixed ionic conductor of claim5.
 16. A fuel cell comprising as a solid-state electrolyte a mixed ionicconductor of claim
 9. 17. A gas sensor comprising as a solid-stateelectrolyte a mixed ionic conductor of claim 9.